3 Answers
3

You can create a custom graph that pulls items from multiple hosts. The graph however will be associated with a host, in which case you could create a phantom host which you can associate the graph with. Configuration -> Hosts -> Graphs (in the host you want the graph to be associated with). When you add your Graph items you can selected the host from which each item comes from.

Alternatively there are aggregate hosts available as well. These allow for the accumulation of items across all hosts in a host group.

note that this is not entirely correct - a graph will only appear for hosts that actually have items included in that graph, thus creating a "phantom" host will not work - graph will never show for that host
–
RichlvNov 17 '14 at 14:03

You can add calculated items to the "phantom" host, which refer to the actual host's items. That way the graph is displayed.
–
FuePiMay 8 at 9:05

Alternative: If your graphs are busy and hard to distinguish multiple hosts, or if you don't want to create the graphs manually, you can also create a screen, and put multiple graphs on the screen each from different hosts (e.g. the standard graphs so you don't have to roll your own).